When a turbocompressor 1 is operated, a high-pressure gaseous refrigerant discharged from this turbocompressor 1 is fed to a condenser 2 wherein the gaseous refrigerant is condensed and liquefied by dissipating heat to a cooling medium, such as cooling water, flowing and passing through a heat transfer tube 3, as illustrated in FIG. 12(A).
Then, this liquid refrigerant flows into an intercooler 4 in which the pressure of the liquid refrigerant is throttled or reduced to an intermediate pressure in a high-pressure-side throttling (or pressure reducing) mechanism 24. Thus, a part of the liquid refrigerant evaporates. Further, liquid drops are separated by an eliminator 26. Thereafter, the vapor is sucked into a high-stage-side impeller 8 of the turbocompressor 1.
The remaining liquid refrigerant is cooled owing to latent heat of the vaporization. Thereafter, the remaining liquid refrigerant is reduced by a low-pressure-side pressure reducing mechanism 25. Thus, the flow rate of the liquid refrigerant is regulated. Simultaneously, adiabatic expansion thereof occurs, so that a low-pressure gas-liquid two-phase flow thereof is obtained.
Then, this refrigerant enters an evaporator 5 wherein this medium evaporates and vaporizes by absorbing heat from cooled media such as brine and cooling water flowing and passing through a heat transfer tube 6 and is changed into a low-pressure gaseous refrigerant. This low-pressure gaseous refrigerant is sucked again into the turbocompressor 1.
Centrifugal impellers 7 and 8 of the turbocompressor 1 are fixedly mounted on an end portion of the rotary shaft 9 in such a manner as to be spaced in the direction of the shaft, and are enclosed in a hermetic housing 10.
Further, a pinion 11 is fixedly mounted on the other end portion of this rotary shaft 9. In a gear chamber 19, the pinion 11 engages with a gear (or wheel) 12 which is fixedly mounted on an output shaft 14 of an induction motor 13.
Rotary shaft 9 of the turbocompressor 1 is supported by bearings 15 and 16 in the gear chamber 19, while the output shaft 14 of the induction motor 13 is supported by bearings 17 and 18.
Oil reservoir 20 is formed in the bottom portion of the gear chamber 19. Lubricating oil stored in the oil reservoir 20 is extracted by an oil pump 21 to an oil cooler 22 wherein the lubricating oil is cooled by allowing the lubricating oil and the cooling medium, which has flowed through the heat transfer tube 23, to perform heat exchange therebetween. Further, after foreign materials are removed from the lubricating oil by a filter 27, the cooled lubricating oil is supplied to and lubricates the pinion 11, the gear 12 and the bearings 15, 16, 17 and 18. Thereafter, the lubricating oil returns to the oil reservoir 20.
Referring now to FIG. 12(B), there is shown Mollier chart (or diagram) of this cooling cycle.
Gaseous refrigerant sucked into the turbocompressor 1 when being in a state A is then brought into a state B by being compressed by means of a low-stage-side impeller 7. Subsequently, the gaseous refrigerant is sucked into the high-stage-side impeller 8 when being in a state C, and is then put into a state D by being compressed.
This gaseous refrigerant is brought into a state E by being cooled by the use of a condenser 2. Subsequently, this refrigerant gas becomes a saturated liquid refrigerant, which is in a state F, by being condensed. This saturated liquid refrigerant is then put into a state G by being reduced by means of the high-pressure-side pressure reducing mechanism 24 of the intercooler 4. Further, a part of this saturated cooling medium evaporates and is brought in a state C and is then sucked into the high-stage-side impeller 8.
The rest of this liquid refrigerant is put into a state H and is further brought into a state I by being reduced by means of the low-pressure-side pressure reducing mechanism 25. This cooling medium becomes put into the state A by evaporating in the evaporator 5, and is then sucked into the turbocompressor 1.
Incidentally, in Mollier chart, reference character J designates a saturated liquid line; and K a saturated vapor line.
However, in the case of the aforementioned conventional turborefrigerator, the rotary shaft 9 of the turbocompressor 1 is supported by bearings 15 and 16. Further, the output shaft 14 of the induction motor 13 is supported by bearing 17 and 18. Furthermore, power of the induction motor 13 is transmitted to the turbocompressor 1 through the gear 12 and the pinion 11. Consequently, the aforesaid conventional turborefrigerator has encountered problems in that the configurations of the turbocompressor 1, a speed-increasing mechanism and the induction motor 13 becomes complex, that not only the dimensions, weight and cost thereof are increased but the mechanical loss thereof is high, and that the coefficient of performance (COP) is low.
Further, the bearings 15, 16, 17 and 18 and the gears 11 and 12 are lubricated by the lubricating oil. Therefore, it is necessary to change the lubricating oil periodically. Moreover, the lubricating oil and the cooling medium cannot be prevented from blending with each other through the rotary shaft 9.
When the temperature and pressure rise, the cooling medium having blended with the lubricating oil evaporates. Thus, there are a fear that the inconveniences, such as the cavitation of the oil pump 21 and the lubrication failure and seizure of the bearings 15, 16, 17 and 18, are caused.
Moreover, when lubricating oil blends with the cooling medium, the heat-transfer-performance of the condenser 2 and the evaporator 5 is degraded. Thus, there is a fear that reduction in the cooling ability, increase in power consumption; abnormal stop of the refrigerator are caused.